What forms the inverted Y on a radiograph?

• A. The floor of the nasal fossa and the anterior border of the maxillary sinus.
• B. The frontal bone and the zygomatic arch.
• C. The alveolar ridge and the palatine bone.
• D. The ethmoid air cells and sphenoid sinus.

Answer: (A)

The inverted Y on a radiograph is formed where the floor of the nasal cavity meets the anterior border of the maxillary sinus. In other words, the boundary that forms the nasal fossa floor and the boundary that forms the front wall of the maxillary sinus intersect to create that upside-down “Y” shape. This radiographic landmark helps identify the maxillary sinus region and distinguish it from the nasal cavity on dental/ skull radiographs. The other choices don’t produce this specific Y-shaped boundary: they involve different skull walls or dental structures that don’t define the maxillary sinus boundary in this way.